(a) Field of the Invention
The present invention relates to a drug delivery system for administering a drug into bodily tissues of a patient, and more particularly, to a novel type of a needle-free drug delivery system in which strong energy such as a laser beam is focused inside liquid contained in a sealed pressure chamber to cause bubble growth and the volume expansion in the sealed pressure chamber due to the bubble growth so as to elongate an elastic membrane, so that an instantaneous pressure is applied to a drug solution contained in a drug microchamber adjacent to the elastic membrane to allow the drug solution to be injected in the form of a liquid microjet, thereby enabling the drug solution to rapidly and accurately penetrate into the bodily tissues of the patient.
(b) Background of the Related Art
In general, a variety of drug delivery systems or methods have been applied as a method for administering a treatment drug into a patient's body in a non-oral manner in a medical field. Among these methods, the most commonly used method is an intracutaneous injection method employing a conventional syringe. However, such an intracutaneous injection method is very effective in that a drug can be directly injected into an internal affected region of a patient, but still entails a great shortcoming in that the patient suffers from an inconvenience of having to feel a pain during the injection. Besides, the intracutaneous injection method encounters many drawbacks in that a wound is caused by the use of a syringe needle, leading to a risk of wound infection, a skilled operator is needed to perform the injection treatment, and in that the re-use of the syringe is difficult, resulting in waste of resources.
Due to the drawbacks of the above-mentioned conventional intracutaneous injection method, many researches have been made to develop a needle-less drug delivery system as a substitute for the conventional intracutaneous injection method. In an attempt to develop the needle-less drug delivery system, there has been proposed a drug delivery system which injects a drug at high velocity in the form of a liquid microjet to allow the drug to directly penetrate into an internal target region through the skin's epidermis.
The research of such a microjet drug delivery system was first attempted in the 1930s. The initial microjet drug delivery system is a very basic drug delivery method using a simple microjet mechanism. The above microjet drug delivery system involves various problems in that there is a risk of cross infection, a splash back phenomenon occurs during the microjet injection, and an accurate penetration depth is difficult to adjust, thereby decreasing reliability. Particularly, since such a conventional microjet drug delivery system still has a disadvantage in that the treatment is accompanied by a considerable pain, it was not widely adopted as an alternative to the conventional intracutaneous injection method.
In addition, as a method for addressing the pain-related problem involved in the above microjet drug delivery system and stabilize the drug administration, Stachowiak et al. has developed and proposed a microjet drug delivery system using a piezoelectric ceramic element (J. C. Stachowiak et al, Journal of Controlled Release 124: 88-97 (2009)). As shown in FIG. 6, the microjet drug delivery system proposed by Stachowiak et al. is one in which a drug is injected at high velocity in the form of a liquid microjet using vibration generated when an electric signal is applied to the piezoelectric ceramic element. According to the microjet drug delivery system to Stachowiak et al., the injected drug can be stably injected intracutaneously into the skin without touching the nervous tissues through a real-time change in injection velocity of the microjet, thereby effectively reducing a pain during the treatment. However, the microjet control of a trace amount of drug must be capable of being performed in order to implement the time-varying monitoring of the drug injection. The microjet drug delivery system using the piezoelectric ceramic element has a great difficulty in realizing an actual drug delivery system due to a limitation of microjet control precision.
In the meantime, besides the above microjet drug delivery system using an electric element and device, according to a recent research result, it has been reported that a microjet drug delivery system using a laser was developed (V. Menezes, S. Kumar, and Takayama, Journal of Appl. Phys. 106, 086102 (2009)). As shown in FIG. 7, such a microjet drug delivery scheme is one in which a laser beam is irradiated onto an aluminum foil to generate a shock wave so that a drug solution is injected in the form of a microjet. The microjet drug delivery scheme has an advantage in that the laser permits high energy to be focused inside a very small area of the drug solution, enabling implementation of a precise level of needle-free drug delivery system. However, the above microjet drug delivery system using the laser beam and the shock wave entails problems in that continuously controlled microjet injection is impossible, and particularly the re-use of the used system is difficult because ablation occurs on the aluminum foil due to the irradiation of the laser beam thereto.